An abnormal chromosome number (aneuploidy) in developing embryos is the leading genetic cause of congenital birth defects and pregnancy loss in women. The majority of aneuploidies are attributed to errors in chromosome segregation that occur during meiotic division in oocytes, and increase significantly with maternal age. Chromosome segregation is critically dependent on assembly of the microtubule spindle apparatus as well as the establishment of stable chromosome-microtubule interactions. Disrupted spindles in oocytes from older women have been recognized for some time, yet the underlying causes remain unknown. Notably, our recent studies in mice demonstrate that disruption of spindle stability can promote chromosome segregation errors, which are not fully resolved -despite activation of the spindle assembly checkpoint (SAC) in oocytes. These findings indicate that defects in spindle stability, which do not promote complete meiotic arrest, likely pose a potentially significant risk in contributing to aneuploidy. Yet, despite its fundamental importance, regulation of spindle assembly/organization in mammalian oocytes is poorly understood. In current studies, we identified a critical role for pericentrin in stable meiotic spindle formation. The experiments outlined in this proposal address the underlying mechanisms of meiotic spindle formation in oocytes, and will test whether these mechanisms are disrupted with increasing maternal age. In Aim 1, we propose to test the function of pericentrin by generating an oocyte-conditional knockdown mouse using an established transgenic RNAi approach. This unique genetic model will be used to test two central questions. (1) Does pericentrin plays a key role in regulating oocyte MTOC organization and function? (2) Is MTOC-mediated microtubule nucleation essential for stable meiotic spindle formation in oocytes? In Aim 2, we propose to determine whether oocytes from older female mice exhibit defects in meiotic spindle organization and/or stability. Importantly we will test if these defects are attributable to alterations in MTOC function or spindle microtubule stability. Knowledge gained from these studies will provide critical insight into the basis of human aneuploidy and provide improved parameters for the analysis of oocyte quality. PUBLIC HEALTH RELEVANCE: An abnormal chromosome number (aneuploidy) in developing embryos is the leading genetic cause of congenital birth defects and pregnancy loss in women. The majority of aneuploidies are attributed to chromosome segregation errors that occur during meiotic division in oocytes, and increase significantly with maternal age. Accurate chromosome segregation is critically dependent on assembly of the microtubule spindle apparatus and the establishment of stable chromosome-microtubule interactions. In this study we propose to (1) assess the underlying mechanisms of meiotic spindle formation and (2) test the hypothesis that defects in meiotic spindle stability contribute to age-associated aneuploidy in oocytes.